Shelf



FIG. 1 is an isometric view showing a shelf;

FIG. 2 is another isometric view thereof;

FIG. 3 is an elevation view thereof;

FIG. 4 is a top plan view thereof; and,

FIG. 5 is a side elevational view thereof.

The broken lines in FIG. 1 depict environmental subject matter only andform no part of the claimed design.

CLAIM The ornamental design for a shelf, as shown and described.